Strange problem with D100 and airspeed

[JimStewart]

D100 has 5.5 firmware, is networked with a D120 and is installed in a 2006 CTSW.

Went flying yesterday evening.  Everything was fine during the flight, no reason to question airspeed until I taxied back to the hangar.  Instead of the airspeed indicator going blank as it normally does, it varied between 15-17 knots.  I stopped the aircraft and it was still varying between 15-17 knots.  I pressed the leftmost button to toggle the display screen and the airspeed field immediately went blank as it should have been. 

 

[Dynon]

Presumably there wasn't a 15ish knot headwind when you were on the ground. Could be a few things. First, water in the pitot or static lines can cause a volume of air to be very slightly pressurized (15 knots are tiny fractions of a PSI, so it doesn't take much). But if you don't think that's it, you can perform a zero pressure calibration under SETUP > SPDCAL when you have the aircraft in a COMPLETELY windless environment. That lets you fine tune the zero airspeed datapoint to what your pressure sensors are seeing. Because low airspeeds are such small pressures, the sensor value that equals no airspeed can drift a bit over time.